The present invention relates in general to metallic filler materials and bears a peripheral relationship to the diffusion bonding arts.
Frequently expensive gas turbine engine components, such as superalloy turbine blades and vanes, are found with small defects resultant from the casting processes or develop small cracks during engine service. Although such defects may be relatively small, they are often sufficient to cause rejection of the component. In many instances, however, the defect is of such a nature that repairs would be satisfactory. However, lacking a suitable means for reliably repairing such defects, these components are often scrapped.
In an attempt to salvage such parts, many repair techniques have been attempted in the past. For example, although repair by fusion welding has occasionally been successful, its success tends to be sporadic, and the welding technique itself often produces additional cracking due to the typical high crack sensitivity of the cast superalloys.
Brazing procedures have also been utilized in attempts to repair defective turbine components. One method has been to simply flow molten braze material into an existing crack. Unfortunately, this technique has been particularly unsuccessful because of unremoved oxides or other contaminants in the cracks or because tight or partially closed crevice areas have prevented a complete fill with braze material. In such cases, although the cracks may be sealed at the surface, no assurance can be provided that subsurface cracks will be sealed as well. This is, of course, not only detrimental but difficult to detect as well.
A more satisfactory approach to component repair is to first eliminate the cracks by mechanically routing out the entire defective area and then refilling it. However, when braze alloys are employed as the filler for such relatively large volumes, upon solidification they often form quantities of eutectic phases which are weak, brittle and prone to adverse selective oxidation during subsequent component service.
Although the desirability of effecting component repairs has long been evident, it is apparent that no satisfactory repair techniques exist, particularly where such repairs can be effected reproducibly and reliably.